Influences and applications of H-type reagent on slurry separation treatment of large-diameter slurry shield

A new H-type dewatering reagent is developed to address the problems of slow dewatering rate of shield waste slurry, high water content of sludge and pollution of wastewater discharge in the construction of Zhanjiang Bay undersea tunnel in Guangdong. Through the flocculation and dewatering tests, micromechanical tests and field production tests, the variation rules of slurry separation volume ratio/supernatant turbidity/grain-size distribution and zeta potential are revealed, and the differences between the H-type reagent and three types of polyacrylamide (PAM) in slurry dewatering effects are comprehensively evaluated. The results show that the optimum addition amount of the H-type reagent is 0.5%. Compared with that of the PAM, the settling rate of the H-type reagent is slower in the early stage, but the water content of the dewatered sludge is reduced by about 18.1%, and the supernatant is very clear, and the pH value of 7.8 meets the condition of direct discharge. The H-type reagent has both better bridging net action and electro-neutralization action, which makes it easier for the fine particles with particle size < 10 μm to aggregate into large particles with particle size > 50 μm, accelerating the flocculation velocity of the slurry. The H-type reagent creates Ca drainage channels with stronger water permeability, reducing the viscosity of the slurry and improving the efficiency of slurry press filtration and dewatering. Compared with the original dewatering reagent, the use of the H-type reagent of 0.1% on site can increase the solid content of de-cemented samples by 30.5% and reduce the project cost by 20%.